The present invention generally relates to, for example, fuel delivery in internal combustion engines.
Internal combustion engines generate power by causing a mixture of air and combustible fuel to ignite and burn in one or more combustion chambers, such as combustion cylinders in an automobile. Conventional internal combustion engines use combustion chambers that have two valve-controlled orifices: one intake orifice/valve for drawing fuel into the combustion chamber and one exhaust orifice/valve for expelling exhaust gas after the air/fuel mixture has ignited and burned. When the intake valve is open (and the exhaust valve is closed), an air/fuel mixture is drawn into the combustion chamber. The time period during which an air/fuel mixture is drawn into the combustion chamber is referred to as the xe2x80x9cintake period.xe2x80x9d Then, the input valve is closed, and the air/fuel mixture is ignited. The force of the air/fuel ignition forces linear motion of a piston slideably disposed in the combustion chamber. Then, the exhaust valve is opened, and exhaust gases generated during the ignition of the air/fuel mixture are expelled from the combustion chamber through the exhaust orifice/valve by the downward motion of the piston. This time period is referred to as the xe2x80x9cexhaust period.xe2x80x9d When the piston reaches the bottom of the combustion chamber, the intake valve is opened (and the exhaust valve is closed), and the cycle is repeated.
In a gasoline engine, it is commonly-known that the fuel ignites and burns most efficiently, thereby minimizing undesirable exhaust emissions, when the average air/fuel ratio in the combustion chamber is 14.7 (known as xe2x80x9cstoichiometryxe2x80x9d). If the average air/fuel ratio in the combustion chamber is significantly less than stoichiometry, then the air/fuel mixture is considered xe2x80x9crichxe2x80x9d and the air/fuel mixture does not burn efficiently. On the other hand, if the average air/fuel ratio in the combustion chamber is significantly greater than stoichiometry, then the air/fuel mixture is considered xe2x80x9cleanxe2x80x9d, and the air/fuel mixture does not ignite and burn fully. As a result, a greater amount of undesirable exhaust emissions are expelled from the combustion chamber.
To improve the fuel efficiency of internal combustion engines, it is desirable to be able to cause the engine to function efficiently with a lean air/fuel ratio during steady-state operation (i.e., when the engine is operated at substantially the same engine speed and load) while, at the same time, minimizing undesirable exhaust emissions. A so-called xe2x80x9clean burnxe2x80x9d engine uses less fuel, since it functions with an air/fuel mixture that includes less fuel than the stoichiometric air/fuel ratio.
A known method for implementing a lean burn engine with known fuel injectors comprises alternatively injecting a lean air/fuel mixture and a rich air/fuel mixture into the combustion chamber during the same intake period. Specifically, for each intake period, a lean air/fuel mixture is injected into the combustion chamber for the majority of the intake period. For a relatively shorter portion of the intake period, a rich air/fuel mixture is injected into the combustion chamber. While the lean air/fuel mixture does not fully ignite and burn on its own, the rich air/fuel mixture ignites immediately and causes the otherwise lean air/fuel mixture in the combustion chamber to fully ignite and burn efficiently. As a result, the average air/fuel ratio during each intake period is lean, resulting in increased overall fuel efficiency. Nonetheless, because the air/fuel mixture burns to completion, the undesirable exhaust emissions are minimized.
Heretofore, the lean burn methodology described above has been implemented in internal combustion engines by using combustion chambers having three orifices/valves: two intake orifices/valves and an exhaust orifice/valve. One intake orifice/valve is used to receive the lean air/fuel mixture into the combustion chamber during most of the intake period, and the second intake orifice/valve is used to receive the rich air/fuel mixture into the combustion chamber during a relatively short portion of the intake period. Thus, the lean air/fuel intake valve is open and the rich air/fuel intake valve is closed for most of each intake period, and the rich air/fuel intake valve is open and the lean air/fuel intake valve is closed for the remaining portion of each intake period. The exhaust valve functions the same as it does in conventional two-valve combustion chambers. In response to control signals generated by an electronic controller, a cam shaft normally controls the opening and closing of the three valves, while a solenoid valve controls the amount of fuel allotted for intake during the intake cycle.
While the above-described method and system for implementing a lean burn engine performs adequately, the use of three-valve combustion chambers is relatively more complicated and expensive than conventional two-valve combustion chambers. Further, the mechanical controls necessary to precisely implement the alternative opening and closing of two intake valves during the same intake period are relatively complicated and difficult to implement. As a result, it would be desirable to have an improved method and system for implementing a lean burn internal combustion engine.
Briefly and in general terms, the present invention relates to a fuel delivery system having a drop ejector for discretely ejecting drops of combustible liquid in a digital manner. A controller is configured to cause the drop ejector to provide a first air/fuel mixture to a combustion chamber for a first portion of a fuel intake period and to provide a second air/fuel mixture to said combustion chamber for a second portion of the same fuel intake period.